Methane potential of fruit and vegetable waste: an evaluation of the semi-continuous anaerobic mono-digestion

The anaerobic digestion (AD) of a high diversity blend of fruit and vegetable waste (FVW) generated in tropical conditions as a single substrate was performed. A continuously stirred tank reactor (CSTR) operated in semi-continuous regime was used for AD. The reactor performance was monitored with gradually increasing organic loading rates (OLRs) from 0.5 up to 5.0 gVS L–1 d–1. The biochemical methane potential (BMP) of FVW determined by batch bottles was 360 LN CH4 kgVS–1, with a biodegradability of 79%. A stable pH with an adequate level of buffering capacity was observed during the entire experiment. Methane yield indicated the best performance at an OLR of 3.0 gVS L–1 d–1, with 285 LN CH4 kgVS–1 added, reaching 79% of BMP. At an OLR over 3.0 gVS L–1 d–1 accumulation of volatile fatty acids (VFA) was detected; in particular, propionic acid was monitored, and a decreased methane yield was detected. Biogas production rate was 1.55 LN L–1 d–1 and showed linear increase according to increases in the OLR.